Method and device for detecting muzzle flash of light firearms

Abstract

The invention comprises using a photodetector that it sensitive in the MWIR band, performing image differencing on two successive images at a time, and defining thresholds for said differences in order to extract only those exceeding the threshold used.

The invention claimed is: 
     
       1. Method for detecting muzzle flashes from light weapons by an infrared matrix photodetector that is sensitive in the mid wave infrared radiation (MWIR) band and reacts to infrared radiation of which the wavelengths are between 3 and 5 μm, the method comprising:
 acquiring, by the infrared matrix photodetector at a frequency of approximately 1000 Hz, successive images of a landscape in which said light weapons may be located, 
 calculating, by the infrared matrix photodetector, differences between each of said images and a preceding image, 
 thresholding, by the infrared matrix photodetector, said image differences by means of a threshold that is at least approximately representative of noise of said landscape, and 
 extracting, by the infrared matrix photodetector, only said differences in image portions that are above said threshold. 
 
     
     
       2. Method according to  claim 1 , wherein the differences in the image portions that are above said threshold are unloaded immediately after thresholding. 
     
     
       3. Method according to  claim 2 , wherein an immediate-unloading frequency of said image differences is approximately 1000 Hz. 
     
     
       4. Method according to  claim 1 , wherein, after thresholding, the differences in the image portions that are above said threshold are stored and collected in a buffer zone. 
     
     
       5. Method according to  claim 4 , wherein an unloading frequency of said image differences outside the buffer zone is less than 1000 Hz. 
     
     
       6. Device for detecting muzzle flashes from light weapons, comprising:
 a sequential infrared matrix photodetector comprising a plurality of photosites, each of which forms a portion of an image of a landscape observed by said photodetector, wherein said photodetector is sensitive in the mid wave infrared radiation (MWIR) band and reacts to infrared radiation of which the wavelength is between 3 and 5 μm, and is capable of acquiring successive images at a frequency of approximately 1000 Hz; and 
 a measuring circuit associated with each of the photosites of said photodetector, the measuring circuit comprising:
 first means for storing the corresponding portion of a current image, 
 second means for storing the corresponding portion of a preceding image, 
 means for discerning a difference between said portion of the current image and said portion of the preceding image, 
 third means for storing said image difference, and 
 means for thresholding said image difference by a threshold that is at least approximately representative of noise of said landscape, and 
 means for unloading only the differences in the image portions that are above said threshold. 
 
 
     
     
       7. Device according to  claim 6 , wherein said first, second and third means for storing comprise capacitors. 
     
     
       8. Device according to  claim 6 , wherein said first and second means for storing are controlled by a transfer register that allows, for each operating sequence of said photodetector, said portion of the current image of a preceding sequence to pass from said first means for storing to said second means for storing. 
     
     
       9. Device according to  claim 6 , wherein said threshold is adjustable in order to be able to be adapted to different landscapes. 
     
     
       10. Device according to  claim 6 , wherein a signal receiver that is arranged in parallel in said measuring circuit is associated with each photosite. 
     
     
       11. A sequential infrared matrix photodetector, said photodetector being sensitive in the mid wave infrared radiation (MWIR) band, reactive to infrared radiation of which the wavelength is between 3 and 5 μm, and capable of acquiring successive images at a frequency of approximately 1000 Hz, the photodetector comprising:
 a plurality of photosites, each of which forms a portion of an image of a landscape observed by said photodetector; and 
 a measuring circuit associated with each of the photosites, wherein the measuring circuit is configured to: (1) discern a difference between signals indicative of a portion of a current image and a portion of a preceding image; (2) compare a threshold to one or more signals indicative of said image difference, the threshold being at least approximately representative of noise of said landscape; and (3) output said image difference signals that are above the threshold.